Experiments on white mice, made with the use or genetically linked pai
r of P. mirabilis differing in the presence of protease activity, have
demonstrated the role of this activity in the aggravation of the infe
ctious process, observed only in cases of the parenteral introduction
of microorganisms. The damaging action of proteases manifests by decre
ased antiprotease capacity of the blood and the dissemination of bacte
ria into organs and tissues with the predominant colonization of the u
rinary tract. The damage of the epithelial barrier of the gastrointest
inal mucosa after the intragastric administration of bacteria can be o
bserved after preliminary destruction of the protective layer consisti
ng of mucin and containing sIgA.